The 1 ns rise-time outputs are generated using diodes to clip a high
amplitude signal. In units with serial numbers less than 1190, GaAs diodes
were used for clipping. After serial number 1190, silicon diodes were used.

The high amplitude output stage of the 106 is made of four 7189A tubes in parallel.
With moderate effort, the socket wiring can be made compatible with the 7189 aka 6BQ5.